Polyolefins have excellent characteristics in processability, mechanical properties, electric characteristics and the like, but involves problem on adhesion due to the low surface energy thereof. Accordingly, improvement of adhesion technique of a polyolefin as a base material, and one example thereof is development of a hot-melt adhesive. A hot-melt adhesive has such advantages that coating and drying steps can be omitted, and no solvent is scattered, as being different from a solvent type adhesive. The techniques shown below have been known as techniques relating to a hot-melt adhesive.
Patent Document 1 discloses a resin for a hot-melt adhesive containing a propylene polymer having a particular stereoregularity and a tackifier resin. Patent Document 2 discloses a reactive hot-melt adhesive containing a urethane prepolymer obtained by reacting a polyolefin resin having a particular functional group as an end group with a polyisocyanate. Patent Document 3 discloses a reactive hot-melt adhesive containing a modified polyolefin modified with an unsaturated carboxylic acid or an anhydride thereof, a polyolefin and an isocyanate compound. Patent Document 4 discloses a reactive hot-melt adhesive containing a urethane prepolymer and a metallocene polyolefin. Patent Document 5 discloses a reactive hot-melt adhesive composition formed by reacting an active hydrogen-containing graft modified material with an excessive amount of a polyisocyanate compound. Patent Document 6 discloses a particular urethane prepolymer composition having an end isocyanate group and a reactive hot-melt adhesive containing the composition. Patent Document 7 discloses modified polyolefin wax modified with a particular silane compound and a method of using the wax in a hot-melt adhesive.
However, all the aforementioned techniques are not necessarily sufficient. For example, an adhesive using the resin disclosed in Patent Document 1 is demanded to be further enhanced in adhesion strength and heat resistance after adhesion to other materials than polypropylene. The polyolefin resin disclosed in Patent Document 2 has a small number of functional groups and thus involves problem upon polymerization through reaction with polyisocyanate, and the resulting reactive hot-melt adhesive involves problem in capabilities, such as heat resistance. The adhesive disclosed in Patent Document 3 requires a high molding temperature and thus involves problem in low-temperature coating property. The adhesive disclosed in Patent Document 4 may suffer phase separation upon melting under heat due to poor compatibility between the urethane prepolymer and the metallocene polyolefin, and thus the usage thereof is restricted. The active hydrogen-containing graft modified material disclosed in Patent Document 5 involves problem in structure and production method thereof, and is demanded to be further improved in curing capability and adhesion strength of the adhesive. The adhesive disclosed in Patent Document 6 involves a problem of poor affinity with polyolefins. The modified polyolefin wax disclosed in Patent Document 7 is of a small modification amount with silane, and thus the adhesive does not have a sufficient curing capability.
As described above, conventional hot-melt adhesives have various problems. In recent years, furthermore, a hot-melt adhesive is further demanded to be improved from the standpoint of environmental issues and work environments, and for example, it is demanded to be able to coated at a relatively low temperature. A hot-melt adhesive that can be coated at a low temperature solves not only the problems in environmental issues and work environments, but also the other problems, for example, the adhesive cannot be used on a base material poor in heat resistance and is liable to be denatured. However, a resin having a high melting point is ordinarily used in the conventional hot-melt adhesives for satisfying the other capabilities. Accordingly, such a hot-melt adhesive is demanded that enables coating at a low temperature with the other capabilities of the adhesive maintained.
[Patent Document 1] WO 01/96490
[Patent Document 2] JP-A-2006-183000
[Patent Document 3] JP-A-51-114438
[Patent Document 4] JP-A-2004-10809
[Patent Document 5] JP-A-9-40930
[Patent Document 6] JP-A-2003-26750
[Patent Document 7] JP-A-2005-68423